The present invention relates to a hole cutter which has a blade cylinder provided on a rotating shaft and a plurality of edge portions arranged side by side at intervals in a rotational direction on an outer periphery of an end portion of the blade cylinder.
Conventionally, edge portions on this kind of hole cutter are provided with a front cutting edge, an inner lateral cutting edge, an outer lateral cutting edge, a front flank, a rake surface, an inner lateral flank and an outer lateral flank. The front cutting edge extends along a radial direction at the leading side along the rotational direction. The inner lateral cutting edge extends along a rotational center line on an inner side of the radial direction. The outer lateral cutting edge extends along the rotational center line on an outer side of the radial direction. The front flank includes the front cutting edge. The rake surface is surrounded by the front cutting edge, the inner lateral cutting edge and the outer lateral cutting edge. The inner lateral flank includes the inner lateral cutting edge. The outer lateral flank includes the outer lateral cutting edge. The front flank and the rake surface constitute an edging angle of the front cutting edge. The edging angle is set to a predetermined value so as to maintain the strength of the edge portion. A rake angle of the rake surface is also set to a predetermined value. When the edging angle and the rake angle have been determined, a front clearance angle of the front flank is determined naturally.
In circumstances where the rake angle is set to the predetermined value, if the front clearance angle is set to a large value, the edging angle is set to a small value. Because of this, the cutting performance of the edge portion is improved. However, an intersecting portion between the front cutting edge and the outer lateral cutting edge is the portion to which a cutting load is most applied when cutting is being started or terminated, and the intersecting portion thus becomes prone to chipping.